The present invention relates to semiconductor device fabrication and, more specifically, to device structures and design structures for a silicon controlled rectifier, as well as methods of fabricating a device structure for a silicon controlled rectifier.
An integrated circuit may be exposed to random electrostatic discharge (ESD) events that can direct potentially large and damaging ESD currents to the integrated circuits of the chip. An ESD event refers to a phenomenon of electrical discharge of a current (positive or negative) for a short duration, during which a large amount of current is provided to the integrated circuit. The high current may be built-up from a variety of sources, such as the human body. Among the sources of exposure to ESD events are the human body described by the Human Body Model, metallic objects described by the Machine Model, and the integrated circuit itself should it charge and discharge to ground as described by the Charged Device Model.
Precautions may be taken to avoid causing ESD events or to protect an integrated circuit from ESD events. One such precaution for protecting the integrated circuit is to incorporate an ESD prevention circuit into the chip. The ESD protection circuit prevents damage to the sensitive devices of the integrated circuits during post-manufacture chip handling and after chip installation on a circuit board or other carrier. If an ESD event occurs, the ESD protection circuit triggers an ESD protection device, such as a silicon-controlled rectifier, to enter a low-impedance, conductive state that directs ESD current to ground and away from the sensitive devices in the integrated circuit on the chip. The ESD protection device clamps the ESD protection device in its conductive state until the ESD current is drained and the ESD voltage is discharged to an acceptable level.
One type of protection device that can be deployed in an ESD protection circuit is a silicon-controlled rectifier (SCR). The SCR is a unidirectional four-layer solid state device utilized in current control applications and includes three electrodes or terminals, namely an anode, a cathode, and a gate, that are distributed among the four layers. In its quiescent state, the SCR restricts current conduction to leakage current. However, a signal applied to the gate that causes the gate-to-cathode voltage to exceed an engineered threshold, known as the trigger voltage, can initiate the conduction of a forward current between the anode and cathode. In response to the triggering signal being removed from the gate, the SCR continues to conduct the forward current so long as the conducted current remains above an engineered holding current. When the conducted current drops below the holding current, the SCR returns to its quiescent state.
Improved device structures and design structures that include a silicon controlled rectifier, as well as fabrication methods, are needed.